Drosophila female oogonial cells may be among the most sensitive germ cell stages in which to assess environmental mutagens and may have considerable bearing on human genetic risk estimates. About one dozen mutagens will be used to evaluate oogonial stem cell sex-linked lethal response. In addition, by analysis (for a few mutagens) the pattern and frequency of mutational clustering in both female and male stem cells, it should be possible to demonstrate whether there is a) a sex-related differential response in equivalent germ cell populations; b) temporal selection for newly induced mutant stem cells; c) "hot spots" with respect to induction sites for recessive lethals recovered from spermatogonia, which are unique cell-viable organism-lethal mutants; and d) develop a comprehensive understanding of the dynamics of mutation induction in the stem cell line of males and females. To carry out these analyses both sex-linked and autosomal recessive lethal techniques will be employed using Drosophila melanogaster.